I have used 2"x3" x8' fir stud lumber. Hemlock is much weaker, not recommended. Should be available at any home/construction supply store. You can burn or bring back home. I use a ~25x25' of that exact Aluminet and it catches a lot more wind than I expected. 2 1/2" drywall-type screws can be driven in if you want along the length of the board to create a point to tie rope to it that won't slip up or down. Also attached to base to a piece of rebar.

Some Seeing Eye - Another question - how big was your aluminet folded down? I've never used aluminet before and we're worried about space in the truck. We're 4 burners coming from Scotland so everything is getting posted to my folks in the Bay Area and we're just going to be doing a dry run the week before the burn when we get there and then packing up. I phoned the supplier we are thinking of getting it from, but they have no idea because their fabricator ships it out direct. We're using an 11' x 21' piece. I know yours was 25' x 25', but if you have even rough dimensions that would be useful.

25x21 feet with sewn edging from Gothic Arch Greenhouses easily fits in a 8100 cubic inch (91 x 38 x 36 cm) x-large Eagle Creek duffelbag. It's springy, compressible, so using "compression straps", available at any outdoor store helps. (You can bring the Aluminet to a SF outdoor store when you arrive to find the right bag. REI is a great supplier common across the USA, but I'm sure there are many options) I have bought cheap Asian duffels, but the zippers separate when you pack the contents. It's extremely lightweight and waterproof so good for attaching by ropes to the top of your vehicle if there is some sort of rack. The duffels go in the washing machine and the Aluminet I hang up outside and wash with a hose after. Enjoy the burn!

Duffels are my preferred international travel packing and for car camping, and the better ones can luggage lock the zipper pull to the end D rings.